Below is a link to one of the demo stills on Tony's website. He uses a brush that is no more than one eighth of an inch wide by a quarter of an inch long, probably smaller. Since brush sizes vary so much by manufactuer I'll tell you that it would be equivalent to using a Trekell brand Golden Taklon nylon watercolor brush in size 1.
He doesn't really stipple then blend. He paints the whole thing with this size brush.
In this shot he is shown doing the chin. First he does the darks in a particular area, and then gradually surrounds the light areas until he has built up the whole rounded form or sub-form, working from dark to light:
http://www.tonyryder.com/demo/opaque/pages/P7300083.htm
If you go to his site and go through all the demo shots (the poster study, the wash-in and the form painting, either one at a time or watch the slide show) you get a pretty good idea of his method.
http://www.tonyryder.com